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C H A P T E R
5 :
W I D E
algorithm. The ODG is the output value from the objective measurement
method that corresponds to the SDG (see Section 2.1) in the subjective domain.
The resolution of the ODG is limited to one decimal. However, be cautious and
do not generally expect that a difference between any pair of ODGs of a tenth
of a grade is significant. The same remark is valid when looking at results from a
subjective listening test. As the right diagram shown in Figure 5.25 , the
ODG can also show positive values. Such values can occur since OPERA™
uses the cognitive model to map the MOVs to the results of subjective listening
tests. In the case of subjective listening tests, the SDG can assume a positive
value, when a test person has incorrectly assigned the reference and test signal.
Distortion Index (DI)
The Distortion Index (DI) has the same meaning as the ODG. However, DI and
ODG can only be compared quantitatively, but not qualitatively. Figure 5.25
shows two curves that represent the relation between the quality and the DI
value (left diagram) and the relation between the quality and the ODG value
(right diagram). As the left diagram demonstrates, the DI is characterized by a
saturation that is less than the saturation of the ODG curve. Furthermore, the
range of values is different. As a general rule, use the ODG as the quality
measure for ODG values greater than approx. –3.6. The ODG correlates very
well with subjective assessments in this range. When the ODG value is less
than –3.6 use the DI.
Note:
Never compare the ODG value of one measurement with the DI
value of another.
DI
-12
+2.61
Figure 5.25: Comparison of the DI and the ODG. Left diagram DI, right diagram ODG
ODG vs. Time
The ODG value in Figure 5.25 an averaged value. Choose the diagram type
"ODG vs. Time" to see the ODG value vs. time. The resulting diagram is shown
in Figure 5.26 . The pink vertical line in the diagram indicates the current
position of the time slider inside the signal.
B A N D
A U D I O
Q U A L I T Y
ODG
-4
-3.6
+0.07
Worse
Quality
103
T E S T I N G
Worse
Quality
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